Protection of immersed metal



atentecl Apr. 25, 1950 PROTECTION OF IMMERSED METAL Herbert Manfred Freud, dit Jean Frasch, Nanterre, France, assignor to Societe De ProduitsChimiques Des Torres Bares, Paris, France No Drawing. Application August3, 1946, Serial 6 Claims.

It is known that ferrous metals corrode (rust) particularly fast whenthey are simultaneously in the presence of oxygen (air) and Water orwater vapor. A steel sheet or iron sheet, for example, plunged intoaerated water, rusts strongly, and more rapidly when warm than cold. Therust propagates itself deeper and deeper, and in a. short time maypierce the sheet, thus often rendering the equipment useless.

In some cases, when the form and use of an apparatus permits it toremain constantly in contact with water, and if the temperature of thewater is not too high, corrosion difiiculties can be averted by suitableprotective coatings, e. g. by painting or by galvanizing the ferrousmetal apparatus or the parts in which water is to be left or which areto be left in contact with water can be so protected. In many cases thisis not, possible. Sometimes the temperature of the water becomes toohigh. Sometimes the form and/or dimensions or use of the piece makespainting impractical (e. g. the inside of tubes or pipes for centralheating, radiators, some types of reservoirs, etc.) Painting theinterior surfaces of such articles being impossible or impractical, thismode of protect ng same is unavailable, and large areas are left whichare subject to rusting. A further objection to painting is that it mustbe repeated, from time to time.

It is well known that notably in the case of ferrous articles to be insubstantially continuous contact with a body of water (i. e. water oraqueous liquid that remains in the circuit, small amounts of water beingadded from time to time to replace evaporation and/or leakage asnecessary) it is a simple matter to add to this water a passivatingagent for the ferrous metal, to protect the latter.

Certain salts are known for this purpose (as passivating agents foriron), e. g. sulphites. When these are added to the water which is toremain in contact with the entire surface of the iron object, theseafford protection, but only as long as the said iron object and waterare to remain, in contact. When the contact ceases (i. e. when the waterand passivating agent are withdrawn from contact with the iron part, c.g. when the water reservoir is emptied or the iron article lifted out ofthe said solution or all or a part of the water has evaporated), rustingmay again commence as to the parts of the ferrous metal no longercovered by such water. Thus of the interior surfaces of radiators (e. g.hot water radiators for heating houses, or automobile radiators) andcooling jackets of various apparatus, the

688,336. In France August 13, 1945 parts which are no longer covered bythe water are subject to rusting.

Other salts, e. g. chromates, used alone, have more durable passivatingaction on iron and steel, but this is insufficient when the water levelfluctuates constantly or frequently, e. g. in automobile radiators.Articles which can resist corrosion (e. g. receptacles) for a longer orshorter period can thus be definitely protected, when kept full of theliquid.

In French patent application P. V. 495,949 of December 28, 1944 (andcorresponding U. S. application 636,067 of December 19, 19-45, nowabandoned, for which latter a substitute case, Ser. No. 126,042 wasfiled on November 7, 1949) I have described a process of protectingmetals aga nst corrosion (including rusting) by forming on their surfacea coating of solution of gelatin or other analogous animal, andinsolubilizing such compound by a tanning agent, such insolubilizationbeing produced by altering the pH of the solution, or by altering theconcentration of the solution, e. g. by evaporating to dryness, andfurther heating if desired.

I have now found that solutions of this kind in addition to theirability to form protective layers as described in said application, alsohave the property of passivating ferrous metal articles of the kindsabove mentioned and can be utilized effectively for the protection ofimmersed metal articles.

The present invention has for its object, a process for protecting suchmetal articles, whether immersed (or in contact with an aqueous liquid)continuously or intermittently, and consists in putting into the liquidbath dissolved gelatin or analogous animal glue material and a tanningagent susceptible of insolubilizing such colloid. As such tanningagents, soluble bichromates are especially suitable for use, and (withthe colloids stated) are highly effective. Accordingly, I add to thewater which is to be in contact with the ferrous metal article(especially when of sheet metal) one of the solutions described in saidapplication 636,067. Or one could add to said water the gelatin and thetanning agent, the pH of said solution, in either case, being such as togive stability to the solution e. g. pH about 4.

I have found that solutions so prepared, even if they are too dilute topermit the formation of protective layers such as those described insaid prior application, have a very great passivating action, and which,if a certain amount of water is added to the solution which bathes themetal article, the latter is protected against corrosion (rusting) notonly while the metal article is in contact with the solution, but alsowhen the solution is partially or wholly removed from contact with saidarticle.

It appears that this passivating action arises from the fact that on thesurface of that portion of the article which is no longer bathed withthe liquid, the evaporating water has left an insoluble film or layer oftanned gelatin (tanned animalglue-like substance) which protects suchsurface.

To giv examples, the following will serve to prevent internal rusting ofan automobile radiator or the radiator of a heating unit.

Example 1 A cooling jacket of an engine which runs all day normallycontains water, e. g. at about 80 C. In place of such Water, a solutionof 8.5 ZnCrzOv and 2.5 gr. of gelatin, per liter of water, isintroduced, to completely fill the jacket and the radiator (enginecooling system). All through the time of running of the engine byaddition of water as needed, from time to time, to replace water lost byevaporation (the engine being running) the cooling system is keptfilled. The heating of the solution produces a certain insolubilizationof the gelatin, which passes from theemulsoid form to the suspensoidform. The micelles of insolubilized gelatin collect on the walls of thejacket and radiator in proportion as the water level therein descends,and protects the so coated area against rusting. When the cooling systemis again filled with water, a part of the insolubilized gelatin becomesseparated from this coating and passes again into the liquid phase, inwhich the iron surfaces completely passive and remain so.

Theoretically, a single filling with th solution should protect thejacket and radiator indefinitely. But practically it is preferable, iithe motor is to be run every day, to discharge the entire solution, g.once a month (more or less) and to then refill the cooling jacket andradiator.

Example '2 Another example of securing momentary protection of metallicreservoirs, during tests for water-tightness, is by immersion in waterfor the period up to the application of painting or var-- nishing thereservoirs. The above solution may be used in place of water.

Thus a receptacle being tested is plunged into a solution containing,per lite of water, 12.8 gr. of ZnCrzOv and 4.5 gr. (dry basis) of stronganimal glue. Air under pressure is introduced into the reservoir, andthe assemblage is watched to see if air bubbles appear (e. g. at anydefective seams, which should then be repaired). The solution, althoughyellowish, is prefectly clear (transparent), so that bubbles can bereadily seen.

If the receptacle is found satisfactory, by this test, the receptacle istaken out, and dried (e. g. in the air), without washing. It will notrust, due to the coating of tanned glue n s surface. and this gives agood external surface to which paint will adhere well.

Other solutions which are disclosed in the pending case 636,067, aresuitable for use in the present invention and should be added to thewater .or aqueous liquid with which the metal article is in constant orintermittent contact.

A satisfactory solution contained 1.5 kg. of gelatin, and the reactionproducts of 4 kg. chromic 4 acid with 2.5 kg. of zinc carbonate, in 100liters of water (pH of solution was 4.25).

Another satisfactory solution was made from 1 kg. gelatin and thereaction product of 3 kg. of chromic acid and 1.95 kg. of manganesecarbonate, in 100 liters of water.

Another satisfactory solution contained 2 kg. gelatin, and thereactionproducts of 8 kg. chromic acid with 4.4 kg. of zinc carbonate in100 liters of Water (pH was 3.9).

Another solution, 2.1 kg. of gelatin, 4 kg. chromic acid and 2.2 kg.manganese carbonate,

' in 100 liters of water, (pl-I of solution was 4).

The invention includes, as new industrial products, the passivatingsolutions or the powders which form same. Such powders contain gelatinor an analogous animal glue and the specified tanning agent for same.These powders can be packaged and sold with simple instructions todissolve same in a stated amount of water and to then apply thesolutions for prevention of rusting, b the methods shown above, toferrous metal articles.

It will be understood that in the above ex?- amples, zinc bichromate,ZnCrzO7, is used as illustrative. Manganese di-chromate could besubstituted. This could be used in the same amount as the zincbichromate. The proportions also can be varied. Thus the solution to beput into contact with the metal surface can contain e. g. from about6.25% to 'lfi% of gelatin or anal; ogous animal glue, about 1% to 10% ofgelatin or analogous glue and the amount of bichromate can vary betweenabout 1% and about 20%. Preferably the amount of bichromate is more thanthe amount of the gelatin or animal glue, e. to one part of gelatin Iprefer to use about 3 to 4 parts of th bichromate.

I claim:

1. A process for suppressing the corrosive action of an aqueous liquidon a metallic surface which is in constant or intermittent contacttherewith, which consists in introducing into such aqueous liquid, agelatinous substance selected from the group consisting of gelatin andan ana ogous animal glue material, and a tanning agent selected from thegroup consisting of the'bichroniates of zinc and-manganese.

2. A. process as covered in claim '1, in which the amount of saidgelatinous material introduced per liter of the aqueous liquid is fromabout 2.5 to 4.5 grams, and in which the tanning agent is ZnCrzOv in anamount of about 8.5 to about 12.8 grams per liter of said aqueousliquid.

A. process of suppressing the corrosive action of an aqueous liqu d on ametallic surface which is in continuous or intermittent contacttherewith, which consists in introducing into such aqueous liquid about0.25% to about 10% of a gelatinous substance selected from the groupconsisting of gelatin and analogous animal glue ma! terials and atanning agent selected from the group consisting of bichromates of zincand of manganese, the amount of said tanning agent I being about 3 toabout 4 times the amount of said geatinous material.

4. A soluble solid. material, suitable for dissolving in water tosuppress its action on metals, such solid material being composedessentially of a gelatinous material selected from the group con.-

sisting of gelatin and analogous animal glue,

mixed with a soluble tanning agent therefor, selected from the groupconsisting of the b1- chromates of manganese and of zinc, such tan niuagent b in pr sent n amount severa t mes 8 greater than the amount 01'said gelatinous ent in amount several times greater than the material.amount of said gelatinous material.

5. In the protection of corrodible metal sur- HERBERT MANFRED FREUD nn'faces from corrosion, by an aqueous liquid, the JEAN FRASCH. step ofdissolving one part of a gelatinous sub- 5 stance selected from thegroup consisting of gel- REFERENCES CITED atin an analgu5 anima1 glue inSaid aqua The following references are of record in the 011s liquid, anddissolving in said aqueous liquid, fil of this patent; an amount of atanning agent selected from the group consisting of the bichromates ofzinc and 10 UNITED STATES PATENTS of manganese, which is about 3 toabout 4 times Number Name Date the amount of said gelatinous substance.1,555,927 Morris Oct. 6, 1925 6. An antirusting solution composedessentially 2,129,459 Benoit Sept. 6, 1938 of water containing insolution a gelatinous ma- 2,148,862 Kern Feb. 28, 1939 terial selectedfrom the group consisting of gel- 15 2,196,128 Stuart Apr. 2, 1940 atinand analogous animal glue, mixed with a soluble tanning agent therefor,selected from the FOREIGN PATENTS group consisting of the bichromates ofmanga- Number Country Date nese and of i c, such ta nin a ent e n pres-492,445 Great Britain Sept. 20, 1933 Certificate of Correction PatentNo. 2,505,535 April 25, 1950 HERBERT MANFRED FREUD, dit JEAN FRASCH Itis hereby certified that error appears in the printed specification ofthe above numbered patent requiring correction as follows:

Column 2, line 19, after the Word animal and before the comma, insertglue; column 4, lines 32 and 33, strike out about 1% to 10% of gelatinor analogous glue; end that the said Letters Patent should be read ascorrected above, so that the same may conform to the record of the casein the Patent Office.

Signed and sealed this 14th day of November, A. D. 1950.

THOMAS F. MURPHY,

Assistant Oommz'ssz'oner of Patents.

1. A PROCESS FOR SUPPRESSING THE CORROSIVE ACTION OF AN AQUEOUS LIQUIDON A METALLIC SURFACE WHICH IS IN CONSTANT OR INTERMITTENT CONTACTTHEREWITH, WHICH CONSISTS IN INTRODUCING INTO SUCH AQUEOUS LIQUID, AGELATINOUS SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF GELATIN ANDAN ANALOGOUS ANIMAL GLUE MATERIAL, AND A TANNING AGENT SELECTED FROM THEGROUP CONSISTING OF THE BICHROMATES OF ZINC AND MANGANESE.